(1) FIELD OF THE INVENTION
This invention relates to a throttle valve opening control device for automatically increasing or reducing the opening of a throttle valve mounted in a suction supply device for supplying air or a mixture of air and field to an internal combustion engine.
(2) DESCRIPTION OF THE PRIOR ART
Generally, in a throttle valve opening control device suitable for use as a constant speed travelling device or an idle speed control device for automotive vehicles, a throttle valve actuator comprising a DC motor and speed reducing gears is used as means for increasing or decreasing the opening of a throttle valve. In this actuator, when an electric pulse is passed to the DC motor to increase or decrease the throttle valve opening, the DC motor is rotated in accordance with the polarity and the duration of the pulse, its rotation being converted through the speed reducing gears to the reciprocatory movement of an output shaft which drives a throttle valve shaft having the throttle valve secured thereto, to thereby control the opening of the throttle valve.
What is most important to this type of throttle valve opening control device and therefore most pined after is to obtain a compact size in throttle valve actuator and to improve its performance. This is considered to be readily understood in view of the fact that this type of throttle valve actuator is mounted in the engine room of an automotive vehicle.